Arrhythmogenicity Test Based on a Human-Induced Pluripotent Stem Cell (iPSC)-Derived Cardiomyocyte Layer

Biomimetic Cardiac Tissue Models for In Vitro Arrhythmia Studies

Cardiac arrhythmias are a major cause of cardiovascular mortality worldwide. Many arrhythmias are caused by reentry, a phenomenon where excitation waves circulate in the heart. Optical mapping techniques have revealed the role of reentry in arrhythmia initiation and fibrillation transition, but the underlying biophysical mechanisms are still difficult to investigate in intact hearts. Tissue engineering models of cardiac tissue can mimic the structure and function of native cardiac tissue and enable interactive observation of reentry formation and wave propagation. This review will present various approaches to constructing cardiac tissue models for reentry studies, using the authors' work as examples. The review will highlight the evolution of tissue engineering designs based on different substrates, cell types, and structural parameters. A new approach using polymer materials and cellular reprogramming to create biomimetic cardiac tissues will be introduced. The review will also show how computational modeling of cardiac tissue can complement experimental data and how such models can be applied in the biomimetics of cardiac tissue.

Human Stem Cells for Cardiac Disease Modeling and Preclinical and Clinical Applications-Are We on the Road to Success?

Cardiovascular diseases (CVDs) are pointed out by the World Health Organization (WHO) as the leading cause of death, contributing to a significant and growing global health and economic burden. Despite advancements in clinical approaches, there is a critical need for innovative cardiovascular treatments to improve patient outcomes. Therapies based on adult stem cells (ASCs) and embryonic stem cells (ESCs) have emerged as promising strategies to regenerate damaged cardiac tissue and restore cardiac function. Moreover, the generation of human induced pluripotent stem cells (iPSCs) from somatic cells has opened new avenues for disease modeling, drug discovery, and regenerative medicine applications, with fewer ethical concerns than those associated with ESCs. Herein, we provide a state-of-the-art review on the application of human pluripotent stem cells in CVD research and clinics. We describe the types and sources of stem cells that have been tested in preclinical and clinical trials for the treatment of CVDs as well as the applications of pluripotent stem-cell-derived in vitro systems to mimic disease phenotypes. How human stem-cell-based in vitro systems can overcome the limitations of current toxicological studies is also discussed. Finally, the current state of clinical trials involving stem-cell-based approaches to treat CVDs are presented, and the strengths and weaknesses are critically discussed to assess whether researchers and clinicians are getting closer to success.

Human Stem Cells for Cardiac Disease Modeling and Preclinical and Clinical Applications—Are We on the Road to Success?

Cardiovascular diseases (CVDs) are pointed out by the World Health Organization (WHO) as the leading cause of death, contributing to a significant and growing global health and economic burden. Despite advancements in clinical approaches, there is a critical need for innovative cardiovascular treatments to improve patient outcomes. Therapies based on adult stem cells (ASCs) and embryonic stem cells (ESCs) have emerged as promising strategies to regenerate damaged cardiac tissue and restore cardiac function. Moreover, the generation of human induced pluripotent stem cells (iPSCs) from somatic cells has opened new avenues for disease modeling, drug discovery, and regenerative medicine applications, with fewer ethical concerns than those associated with ESCs. Herein, we provide a state-of-the-art review on the application of human pluripotent stem cells in CVD research and clinics. We describe the types and sources of stem cells that have been tested in preclinical and clinical trials for the treatment of CVDs as well as the applications of pluripotent stem-cell-derived in vitro systems to mimic disease phenotypes. How human stem-cell-based in vitro systems can overcome the limitations of current toxicological studies is also discussed. Finally, the current state of clinical trials involving stem-cell-based approaches to treat CVDs are presented, and the strengths and weaknesses are critically discussed to assess whether researchers and clinicians are getting closer to success.

Novel Molecular Vehicle-Based Approach for Cardiac Cell Transplantation Leads to Rapid Electromechanical Graft-Host Coupling

Myocardial remodeling is an inevitable risk factor for cardiac arrhythmias and can potentially be corrected with cell therapy. Although the generation of cardiac cells ex vivo is possible, specific approaches to cell replacement therapy remain unclear. On the one hand, adhesive myocyte cells must be viable and conjugated with the electromechanical syncytium of the recipient tissue, which is unattainable without an external scaffold substrate. On the other hand, the outer scaffold may hinder cell delivery, for example, making intramyocardial injection difficult. To resolve this contradiction, we developed molecular vehicles that combine a wrapped (rather than outer) polymer scaffold that is enveloped by the cell and provides excitability restoration (lost when cells were harvested) before engraftment. It also provides a coating with human fibronectin, which initiates the process of graft adhesion into the recipient tissue and can carry fluorescent markers for the external control of the non-invasive cell position. In this work, we used a type of scaffold that allowed us to use the advantages of a scaffold-free cell suspension for cell delivery. Fragmented nanofibers (0.85 µm ± 0.18 µm in diameter) with fluorescent labels were used, with solitary cells seeded on them. Cell implantation experiments were performed in vivo. The proposed molecular vehicles made it possible to establish rapid (30 min) electromechanical contact between excitable grafts and the recipient heart. Excitable grafts were visualized with optical mapping on a rat heart with Langendorff perfusion at a 0.72 ± 0.32 Hz heart rate. Thus, the pre-restored grafts' excitability (with the help of a wrapped polymer scaffold) allowed rapid electromechanical coupling with the recipient tissue. This information could provide a basis for the reduction of engraftment arrhythmias in the first days after cell therapy.

Polymer Kernels as Compact Carriers for Suspended Cardiomyocytes

Induced pluripotent stem cells (iPSCs) constitute a potential source of patient-specific human cardiomyocytes for a cardiac cell replacement therapy via intramyocardial injections, providing a major benefit over other cell sources in terms of immune rejection. However, intramyocardial injection of the cardiomyocytes has substantial challenges related to cell survival and electrophysiological coupling with recipient tissue. Current methods of manipulating cell suspensions do not allow one to control the processes of adhesion of injected cells to the tissue and electrophysiological coupling with surrounding cells. In this article, we documented the possibility of influencing these processes using polymer kernels: biocompatible fiber fragments of subcellular size that can be adsorbed to a cell, thereby creating the minimum necessary adhesion foci to shape the cell and provide support for the organization of the cytoskeleton and the contractile apparatus prior to adhesion to the recipient tissue. Using optical excitation markers, the restoration of the excitability of cardiomyocytes in suspension upon adsorption of polymer kernels was shown. It increased the likelihood of the formation of a stable electrophysiological coupling in vitro. The obtained results may be considered as a proof of concept that the stochastic engraftment process of injected suspension cells can be controlled by smart biomaterials.

Cyclophosphamide arrhythmogenicitytesting using human-induced pluripotent stem cell-derived cardiomyocytes

Cyclophosphamide (CP) is an anticancer drug, an alkylating agent. Cardiotoxicity of CP is associated with one of its metabolites, acrolein, and clinical cardiotoxicity manifestations are described for cases of taking CP in high doses. Nevertheless, modern arrhythmogenicity prediction assays in vitro include evaluation of beat rhythm and rate as well as suppression of cardiac late markers after acute exposure to CP, but not its metabolites. The mechanism of CP side effects when taken at low doses (i.e., < 100 mg/kg), especially at the cellular level, remains unclear. In this study conduction properties and cytoskeleton structure of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) obtained from a healthy donor under CP were evaluated. Arrhythmogenicity testing including characterization of 3 values: conduction velocity, maximum capture rate (MCR) measurements and number of occasions of re-entry on a standard linear obstacle was conducted and revealed MCR decrease of 25% ± 7% under CP. Also, conductivity area reduced by 34 ± 15%. No effect of CP on voltage-gated ion channels was found. Conduction changes (MCR and conductivity area decrease) are caused by exposure time-dependent alpha-actinin disruption detected both in hiPSC-CMs and neonatal ventricular cardiomyocytes in vitro. Deviation from the external stimulus frequency and appearance of non-conductive areas in cardiac tissue under CP is potentially arrhythmogenic and could develop arrhythmic effects in vivo.

Formation of an electrical coupling between differentiating cardiomyocytes

Human induced pluripotent stem cell–derived cardiomyocytes (hiPSC-CMs) serve as an indispensable platform for the study of human cardiovascular disease is human induced pluripotent stem cell–derived cardiomyocytes (hiPSC-CMs). While the possibility of reproducing rare pathologies, patient-specific selection of drugs, and other issues concerning single cardiomyocytes have been well studied, little attention has been paid to the properties of the whole syncytium of CMs, in which both the functionality of individual cells and the distribution of electrophysiological connections between them are essential. The aim of this work is to directly study the ability of hiPSC-CMs to form a functional syncytium that can stably conduct an excitation wave. For that purpose, syncytium forming hiPSC-CMs were harvested and seeded (transferred) on a new substrate on different days of differentiation. The excitation conduction in a sample was characterized by the stability of the wavefront using optical mapping data. We found that the cells transferred before the 20th day of differentiation were able to organize a functional syncytium capable of further development and stable excitation conduction at high stimulation frequencies, while the cells transferred after 20 days did not form a homogeneous syncytium, and multiple instabilities of the propagating wavefront were observed with the possibility of reentry formation.

The Use of iPSC-Derived Cardiomyocytes and Optical Mapping for Erythromycin Arrhythmogenicity Testing

Erythromycin is an antibiotic that prolongs the QT-interval and causes Torsade de Pointes (TdP) by blocking the rapid delayed rectifying potassium current (I_Kr) without affecting either the slow delayed rectifying potassium current (I_Ks) or inward rectifying potassium current (I_K1). Erythromycin exerts this effect in the range of 1.5-100 μM. However, the mechanism of action underlying its cardiotoxic effect and its role in the induction of arrhythmias, especially in multicellular cardiac experimental models, remain unclear. In this study, the re-entry formation, conduction velocity, and maximum capture rate were investigated in a monolayer of human-induced pluripotent stem cell (iPSC)-derived cardiomyocytes from a healthy donor and in a neonatal rat ventricular myocyte (NRVM) monolayer using the optical mapping method under erythromycin concentrations of 15, 30, and 45 μM. In the monolayer of human iPSC-derived cardiomyocytes, the conduction velocity (CV) varied up to 12 ± 9% at concentrations of 15-45 μM as compared with that of the control, whereas the maximum capture rate (MCR) declined substantially up to 28 ± 12% (p < 0.01). In contrast, the tests on the NRVM monolayer showed no significant effect on the MCR. The results of the arrhythmogenicity test provided evidence for a "window" of concentrations of the drug (15-30 μM) at which the probability of re-entry increased.

Cell Culture Platforms with Controllable Stiffness for Chick Embryonic Cardiomyocytes

For several years, cell culture techniques have been physiologically relevant to understand living organisms both structurally and functionally, aiming at preserving as carefully as possible the in vivo integrity and function of the cells. However, when studying cardiac cells, glass or plastic Petri dishes and culture-coated plates lack important cues that do not allow to maintain the desired phenotype, especially for primary cell culture. In this work, we show that microscaffolds made with polydimethylsiloxane (PDMS) enable modulating the stiffness of the surface of the culture substrate and this originates different patterns of adhesion, self-organization, and synchronized or propagated activity in the culture of chick embryonic cardiomyocytes. Thanks to the calcium imaging technique, we found that the substrate stiffness affected cardiomyocyte adhesion, as well as the calcium signal propagation in the formed tissue. The patterns of activity shown by the calcium fluorescence variations are reliable clues of the functional organization achieved by the cell layers. We found that PDMS substrates with a stiffness of 25 kPa did not allow the formation of cell layers and therefore the optimal propagation of the intracellular calcium signals, while softer PDMS substrates with Young’s modulus within the physiological in vivo reported range did permit synchronized and coordinated contractility and intracellular calcium activity. This type of methodology allows us to study phenomena such as arrhythmias. For example, the occurrence of synchronized activity or rotors that can initiate or maintain cardiac arrhythmias can be reproduced on different substrates for study, so that replacement tissues or patches can be better designed.